While in Vancouver, waiting for a friend at the Waterfront ferry station, we entered the Simon Fraser University bookshop across the street. This was a most disconcerting experience in that the bookstore contained essentially no book! Just a tiny bookshelf with local authors and another one with a medley of genres. Including Gaiman’s The Ocean at the End of the Lane. Which I bought against my better judgement as I had tried to read American Dogs years ago and failed. (But liked very much Neverwhere, again a chance occurrence on a bookstore shelf!) As I started reading the book on the ferry to Vancouver Island, hence on the Pacific Ocean!, I first thought this was about the author’s childhood in rural Sussex, with no other friends than his books, finding some ways to relate to the story of a modest household in the early 60’s, only to be interrupted by three whales swimming along the ferry route. The cheek of them! When I picked up the short novel later in Tofino (with Tonkin Beach above), reality started to unravel (in the book!) and horror to creep in (!). Without getting into spoilers, the other world or old country starts appearing to the narrator, a seven year old, with about everything taking another and sinister meaning. And no-one else in his household paying any attention to his warnings. What I really enjoy in the book is the sheer ambiguity of the tale, where one cannot be sure this is pure fantasy made up by a lonely seven year old who strongly dislikes a new nanny and is impacted by his parents’ relationship, or an opening into that alternate reality and its dangers that he and only he is able to enter. The book never concludes and this is a strength of the story. Which works for both adult and children readers. It also reminded me of Miyazaki’s Chihiro Spirited Away (千と千尋の神隠し), in that the supernatural beings here and there are neither evil nor good but simply utterly alien. (This fantastic² movie is considered by my daughter as the most traumatic one she ever saw as a child!) Concluding about the book, this was a very good read, somewhat on the light side although full of forking paths.

The notion of anchoring found in this paper is to allocate specific observations to specific components. These observations are thus anchored to these components. Among other things, this modification of the sampling model implies a removal of the unidentifiability problem. Hence formally of the label-switching or lack thereof issue. (Although, as Peter Green repeatedly mentioned, visualising the parameter space as a point process eliminates the issue.) This idea is somewhat connected with the constraint Jean Diebolt and I imposed in our 1990 mixture paper, namely that no component would have less than two observations allocated to it, but imposing which ones are which of course reduces drastically the complexity of the model. Another (related) aspect of anchoring is that the observations that are anchored to the components act as parts of the prior model, modifying the initial priors (which can then become improper as in our 1990 paper). The difficulty of the anchoring approach is to find observations to anchor in an unsupervised setting. The paper proceeds by optimising the allocations, which somewhat turns the prior into a data-dependent prior since all observations are used to set the anchors and then used again for the standard Bayesian processing. In that respect, I would rather follow the sequential procedure developed by Nicolas Chopin and Florian Pelgrin, where the number of components grows by steps with the number of observations.